1. Field of the Invention
This invention relates to a security document such as a bank note, security, ID card or the like with a security element having at least one mechanically testable magnetic layer and at least one further layer.
2. Description of the Related Art
It has been known for some time to provide security documents such as bank notes or ID cards with magnetic security elements. German patent no. 16 96 245 discloses for example an antifalsification paper in which a security thread with a ferromagnetic coating is embedded. The customarily used magnetic material has a very dark body color, however, so that the security thread is recognizable as a dark strip on the paper surface even when embedded completely in the paper. In order to avoid this disadvantage German patent no. 16 96 245 already proposes additionally providing the thread coated with magnetic material with an opaque white coating on both sides to avoid the optical effect of the magnetic material on the paper surface.
It is further known from German patent no. 27 54 267 to equip a security thread with a magnetic coating and a further security feature. An important selection criterion for the security features to be combined is that the features not be readily recognizable and imitable for a forger. For this reason the magnetic layer is combined for example with a metal layer or an opaque lacquer fluorescent under UV light. However, the measures described in German patent no. 27 54 267 only increase forgery-proofness in case the document is actually checked by machine. The described security features do not, or not readily, permit visual checking of the document""s authenticity.
Therefore, a security thread has also been proposed (WO92/11142) which permits both a mechanical check of magnetic properties and a visual authenticity check. In this case the magnetic layer is combined with an opaque metal layer having gaps in the form of characters or patterns, the magnetic layer being disposed under the metal layer, as regarded by the viewer, so that the optical effect of the magnetic material does not appear on the paper surface. The gaps are virtually unrecognizable in the paper in reflected light but stand out in high contrast from their opaque surroundings in transmitted light. This presupposes, however, that the left-out areas of the characters are transparent, i.e. there must be no magnetic material in the area of the characters. When producing the security element one must therefore make sure that the magnetic layer and visually recognizable characters are produced in register with each other so that they do not overlap.
The invention is based on the problem of proposing a security document with a security element which has a magnetic coating whose inherent color hardly appears in reflected light and which can be provided with additional visually testable features in a simple way.
It has surprisingly turned out that a cover layer semitransparent in the visual spectral region already suffices to weaken the dark appearance of the magnetic material so as to avoid the usually undesirable optical effects. The semitransparent cover layer additionally makes it possible to provide the security element with visually and/or machine recognizable information, e.g. by providing gaps in the form of characters in the magnetic layer or forming the magnetic layer itself in the form of visually and/or machine recognizable characters or patterns. No exactly registered arrangement of cover layer and magnetic layer is necessary any longer in this case since the visually recognizable information is recognizable through the semitransparent layer.
In its simplest embodiment, the security element therefore consists of a magnetic layer and a semitransparent layer covering the magnetic layer.
According to a preferred embodiment, the semitransparent layer consists of a thin semitransparent metal layer. With sufficient layer thickness, a semitransparent metal layer has optical reflection properties which are very similar to an opaque metal layer.
This can be utilized advantageously in the production of security threads, which are usually embedded at least partly in antifalsification paper. In the areas where the thread is embedded completely in the paper it is hardly recognizable on the paper surface in reflected light since the magnetic layer is covered sufficiently by the metal layer. In transmitted light, however, the thread appears as a dark strip in high contrast with the surroundings like an opaque metallic thread.
Instead of a contiguous semitransparent metal layer, one can of course also use other semitransparent materials or layers, such as printing inks with optically variable interference layer pigments, liquid crystal layers or diffraction structures with a semitransparent reflecting layer.
According to a further preferred embodiment, the semitransparent layer of the security element is formed by a screened layer, the individual screen elements being opaque, preferably metallic. The screen elements can have any desired form. One can use standard geometric shapes such as dots, lines, triangles, etc., as well as special patterns, numbers, letters, etc. The screen width is selected so as to effect a sufficient cover of the magnetic layer while any information present under the screened layer simultaneously also remains recognizable. The screen elements can be produced with the aid of any printing ink, but preferably a white or light ink, or by any coating methods, such as vapor deposition, hot embossing, etc.
The magnetic layer can be provided either all over or only in certain areas independently of the kind of cover layer used. According to a preferred embodiment, the magnetic layer is applied in the form of a coding, in particular a bar code. However, the magnetic layer can also contain only gaps in the form of visually and/or machine recognizable characters. Additionally, further visually and/or machine recognizable information can be disposed in the magnetic layer free areas of the code or in the gaps.
According to a special embodiment, the magnetic layer free areas can be filled for example with a nonmagnetic layer having the same color as the magnetic material. This additionally disguises the presence of a magnetic code. This nonmagnetic layer can also have gaps in the form of characters, patterns, etc.
The inventive combination of a magnetic layer and a semitransparent cover layer makes it possible not only to provide testable information in the magnetic layer, however, but also to include the semitransparent cover layer in the design of the security element. This yields a great variety of embodiments which have, along with various specific advantages, the common advantage of increasing the forgery-proofness of the security element or the object provided with this security element.
The security element can, as mentioned above, be formed as a security thread or planchets which are incorporated at least partly into a security document. It is also conceivable, however, to form the security element in a band or label shape and fasten it to the surface of an object. These objects can likewise be security documents. However, the inventive security element can also be used very advantageously in the field of product protection. In this case the security element can have, besides the inventive magnetic layer and semitransparent cover layer, further antitheft elements such as a coil. According to a further variant, the security element can also be provided on or in a document material which is in turn applied to any-shaped objects for product protection.